1. Field of the Invention
This invention relates to projectiles such as bullets and shotgun shot made from a composition containing a specific mixture of tungsten and iron.
2. Brief Description of the Art
Ingestion of expended lead shot by birds, particularly water fowl, has been said to pose a problem in the wild. In indoor shooting ranges, vaporized lead-containing primer powder and vapors from lead bullets is also of concern. Disposal of lead-contaminated soil and sand from shooting ranges is expensive, since lead is a hazardous material. Accordingly, various attempts have been made to find alternatives or substitutes for lead bullets and lead shot.
U.S. Pat. No. 4,428,295 (with Urs as the named inventor and assigned to Olin Corporation) is drawn to high density shot formed by the compaction of two different metallic powders, a first one of the powders having a density greater than lead and the second one being formable under compaction to serve as a binder. In a preferred embodiment, the first powder is tungsten and the second powder is lead.
U.S. Pat. No. 4,949,645 (assigned to Royal Ordnance) discloses shot formed by compacting and sintering a mixture of tungsten, nickel and copper powders.
Statutory Invention Registration H1235 (with Canaday as the named inventor) discloses a tungsten base armor-piercing projectile containing a tungsten carbide alloy.
The use of tungsten-iron mixtures in projectiles is also known. For example, U.S. Pat. No. 5,264,022 (with Haygarth as the named inventor) is directed to high specific gravity, non-toxic, lead-free shotshell pellets consisting of an alloy of iron and tungsten, wherein the content of tungsten is 30% to 46% by weight. This Haygarth patent discloses that tungsten and iron are heated to a temperature above 1,637.degree. C. forming a molten metal mixture. The molten metal is passed through a refractory sieve having holes of a desired diameter to generate molten droplets. These droplets flow through a shot column having first a gas portion to solidify the droplets as spheres and, second, a liquid portion to cool the droplets.
Federal Cartridge Company also made an application to the U.S. Fish and Wildlife Service for the review and approval of sintered tungsten-iron shot as a non-toxic shot dated Aug. 19, 1996. According to this application, the shot proposed by Federal is a sintered powder metallurgical product containing tungsten and iron with a typical tungsten range of 38% to 42% by weight, with the balance of the mixture being iron. The proposed manufacturing process for this shot has the steps of: (1) combining tungsten and iron; (2) sintering at a temperature of 1,520.degree. C.; and (3) bringing the sintered powder metallurgy product to thermal equilibrium. The Federal Application identifies a two-phase material, which is formed with the first phase being a solid solution of tungsten and ferritic iron and the second phase being an intermetallic compound Fe.sub.7 W.sub.6. The Federal Application further states that the shot can be picked up with a magnet.
U.S. Pat. No. 5,339,187 (with Mravic et al. as the named inventors and assigned to Olin Corporation) is directed to frangible lead-free bullets having a density similar to that of lead comprising a compacted composite containing a high-density first constituent selected from the group consisting of tungsten, tungsten carbide, ferro-tungsten and mixtures thereof; and a lower density second constituent selected from the group consisting of tin, zinc, aluminum, iron, copper, bismuth and mixtures thereof, wherein the density of said lead-free bullet is in excess of 9 grams per cubic centimeter and said lead-free bullet deforms or disintegrates at a stress of less than about 45,000 psi.
Separately, Sykes (W. P. Sykes, Trans. AIME, Vol. 73, 1926) teaches that when a molten alloy of tungsten and iron having less than 29.3% by weight tungsten is rapidly cooled from the solid solution temperature region just below the solidus down to room temperature, there will be insufficient time for a precipitation of a second-phase iron tungsten intermetallic particles, and the resulting cooled material will be a solid solution of these two metals. In contrast, Sykes found that slow cooling down to room temperature or a short heat treatment after rapid cooling will cause the formation of these intermetallic particles.
It has now been found that tungsten-iron compositions having a relatively low tungsten content and a relatively high tungsten plus iron content can provide suitable properties (e.g., hardness, ductility, and density) for use as different types of projectiles. That discovery has lead to the following invention.